1. Field of the Invention
The invention relates to a method for the treatment of plant material to provide a protein-rich product and oil relatively free of gossypol.
2. Description of the Prior Art
Gossypol is a known poisonous pigment found in plant material such as cottonseed and has been the object of prior schemes for removal therefrom. Previous attempts to remove gossypol from cottonseed products have included extraction with non-aqueous organic solvents such as hexane and other petroleum fractions, and/or with aqueous monohydric alcohols such as ethanol and isopropyl alcohol.
Sen Gupta [U.S. Pat. Nos. 4,062,882 and 4,533,501] and Iwama [Membrane, vol. 11, no. 2 (1986), pp. 99-108] described desliming processes for the removal of phospholipids from cottonseed and other vegetable oils by extraction with non-aqueous, non-alcoholic organic solvents such as hexane. According to the disclosed processes, the oil was contacted with the solvent to form a miscella, from which the phospholipids therein could be separated by reverse osmosis or ultrafiltration yielding a retentate stream containing the phospholipids, and by a permeate stream of the oil and solvent. In later work, Sen Gupta et al. [Fette Seifen Anstrichmittel, vol. 88, no. 3 (1986), pp. 79-86] disclosed that gossypol could be removed with the phospholipids by substantially the same process.
Lawhon et al. [Journal of Food Process Engineering, vol. 1 (1977), pp. 15-35] disclosed processes for the recovery of residual protein from cottonseed wheys. In the course of protein isolation from dry cottonseed flour by contacting with water, a cottonseed whey was obtained containing residual proteins in addition to smaller molecular weight components (i.e., carbohydrates, salts, amino acids and short-chain peptides). The content of oil and gossypol in the whey was described as negligible.
Ultrafiltration of the whey yielded a retentate stream containing the protein, and a permeate stream which, when subsequently subjected to reverse-osmosis, yielded a retentate stream of the smaller molecular weight components and a permeate stream of water.
As mentioned above, the use of aqueous monohydric alcohol solvents has also been described in the prior art for the extraction of gossypol and/or oil from cottonseed as, for example, in Karnofsky [U.S. Pat. No. 4,144,229], Harris et al. [Journal of the American Oil Chemists' Society, vol. 24 (1947), pp. 370-375]or Rao et al. [JAOCS, vol. 35 (1958), pp. 277-281]. Although each of the references described the formation of a miscella composed of the oil, solvent, and gossypol after extraction of the cottonseed flakes with the solvent, the components of the miscella were separated by phase separation, liquid/liquid extraction, or evaporation. The prior art did not disclose the use of reverse-osmosis and selective adsorption for the separation of these components of the miscella.